Forest Investment Account

Abstract of FIA Project Y051210

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Sulphur fertilization of lodgepole pine: a stable isotope tracer study

Author(s): Sanborn, Paul
Imprint: Prince George, B.C. : University of Northern British Columbia, 2005
Subject: Forest Investment Account (FIA), Pinus Contorta, British Columbia, Growth, Fertilizers
Series: Forest Investment Account (FIA) - Forest Science Program


Sulphur (S) deficiencies in lodgepole pine are widespread in the B.C. central interior, but there is an insufficient basis for prescribing fertilization treatments with both immediate and sustained growth responses. This project builds on the Ministry of Forestsí fertilization research program and careful pilot studies, to combine area-based fertilization response methods with stable isotope tracing of the uptake and fate of S fertilizers. Both elemental S and more immediately plant-available sulphate-S forms are being compared, at operationally realistic addition rates and in combination with nitrogen fertilization. Using two sites that represent typical site and climate conditions in the Sub-Boreal Spruce zone, with low total S concentrations throughout the soil profile, we are comparing relative uptake of these forms, their mobility and tranformations in the soil, and their effects on tree growth. This research will give silviculturists a credible scientific foundation for making better fertilization decisions, and demonstrate serious intent to examine the effects of intensive forest management in B.C. Two growing seasons after fertilization, both foliar concentrations and stable isotope data indicated that sulphate-S was more readily available than elemental S to lodgepole pine. Addition of N (with or without added S) produced little or no improvement to radial growth, perhaps due to induced deficiencies of B and/or K. At Kenneth Creek, two forms of elemental S were applied, and the granulated form containing finely-ground primary particles was more effective at maintaining adequate N/S ratios. Total S and sulphate-S concentrations in litter, FH horizons, and mineral soil suggested that fertilizer sulphate S was more rapidly leached through the forest floor and mineral soil horizons, while elemental S appeared to be largely retained in the forest floor. These interpretations were corroborated by the S isotopic signatures of these soil components. Similar contrasts in soil S distribution were still apparent 12 years after ammonium sulphate and elemental S were applied in an older lodgepole pine fertilization trial in Vanderhoof Forest District. Forest floor S mineralization rates (open system aerobic incubation) and foliar sulphate-S concentrations were significantly higher in plots treated with elemental S relative to controls and plots treated with an identical rate of S application in the form of ammonium sulphate. In contrast, at another site near Williams Lake, lodgepole pine foliar total S and sulphate-S concentrations remained elevated 12 years after a single ammonium sulphate application. Additional analyses of Fe, Al, and Si constituents in soil profiles from the Kenneth Creek, Holy Cross, and Cluculz Creek sites suggested that relatively low concentrations of these weathering products are present, and may limit the capacity for sulphate adsorption.

For further information, please contact Paul Sanborn, University of Northern British Columbia (

Updated September 08, 2005 

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